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Rifles, Reloading, Optics, Equipment
Reloading
Bullet Jump/Jammed - Is it the Bullet design or the rifle
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<blockquote data-quote="Dragoon300" data-source="post: 1984243" data-attributes="member: 115285"><p>I think the answer to your question is simpler than we want it to be. I am a machine design engineer by trade, and live in the precision machining world. I also enjoy shooting, and even more tinkering with my guns. In my experience with my primary precision rifle, a Desert Tech SRS 338 Lapua, I wanted to utilize all of the case capacity while using Berger 300 grain OTM bullets. I wanted to seat the bullet so the boat tail shank junction was at the case neck shoulder junction giving me the most capacity and the full neck for retention and bearing surface. Then I throated the chamber to give me .010" off the rifling so as to not jam the bullet into the rifling because I need to be able to unload without leaving the bullet in the chamber, simple as that. The OTM Hybrids are supposed to be "more tolerant" to jump and I must say that is true in my case, I did not see any real difference initially in testing, and now after 800 plus rounds with the throat eroded .020" more the accuracy is still 1/4 MOA. Mechanically the design shape of the bullet and the lead into the rifling are what make jump more or less tolerable. The benchrest guy's jam their bullets into the rifling because it is more accurate, as the bullet is started into the rifling before ignition. Practical shooters can't do this because they could induce a problem no one wants during unloading, so they must stay back some amount. Manufacturers design more throat into a rifle cartridge to allow for a greater range of bullets, but I believe mostly to reduce pressure as in Weatherby magnums and Remington ultra magnums where they have .300" to .400" to be safe. If you take a .300 ultra mag and load it with a 110 grain bullet it will space walk before entering the rifling. This is the other end of the spectrum from the benchrest guy's! So, I can only say what I know to be true in my case, I had lots of bearing contact in the case neck and only .010" to the rifling (when new) and this helps. I just had Dave Manson make a reamer to my specifications for my Lapua, and one for a 6.5 PRC with Berger 156 grain EOL's and plan on doing the same. I will see how it works out, but am quite sure it will with .010" jump and tuning my load to suit. Hope I didn't get too long winded and this helps.</p></blockquote><p></p>
[QUOTE="Dragoon300, post: 1984243, member: 115285"] I think the answer to your question is simpler than we want it to be. I am a machine design engineer by trade, and live in the precision machining world. I also enjoy shooting, and even more tinkering with my guns. In my experience with my primary precision rifle, a Desert Tech SRS 338 Lapua, I wanted to utilize all of the case capacity while using Berger 300 grain OTM bullets. I wanted to seat the bullet so the boat tail shank junction was at the case neck shoulder junction giving me the most capacity and the full neck for retention and bearing surface. Then I throated the chamber to give me .010" off the rifling so as to not jam the bullet into the rifling because I need to be able to unload without leaving the bullet in the chamber, simple as that. The OTM Hybrids are supposed to be "more tolerant" to jump and I must say that is true in my case, I did not see any real difference initially in testing, and now after 800 plus rounds with the throat eroded .020" more the accuracy is still 1/4 MOA. Mechanically the design shape of the bullet and the lead into the rifling are what make jump more or less tolerable. The benchrest guy's jam their bullets into the rifling because it is more accurate, as the bullet is started into the rifling before ignition. Practical shooters can't do this because they could induce a problem no one wants during unloading, so they must stay back some amount. Manufacturers design more throat into a rifle cartridge to allow for a greater range of bullets, but I believe mostly to reduce pressure as in Weatherby magnums and Remington ultra magnums where they have .300" to .400" to be safe. If you take a .300 ultra mag and load it with a 110 grain bullet it will space walk before entering the rifling. This is the other end of the spectrum from the benchrest guy's! So, I can only say what I know to be true in my case, I had lots of bearing contact in the case neck and only .010" to the rifling (when new) and this helps. I just had Dave Manson make a reamer to my specifications for my Lapua, and one for a 6.5 PRC with Berger 156 grain EOL's and plan on doing the same. I will see how it works out, but am quite sure it will with .010" jump and tuning my load to suit. Hope I didn't get too long winded and this helps. [/QUOTE]
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Bullet Jump/Jammed - Is it the Bullet design or the rifle
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